Which one of the following statements is not true?

1. Tapetum helps in the dehiscence of anther
2. Exine of pollen grains is made up of sporopollenin
3. Pollen grains of many species cause severe allergies
4. Stored pollen in liquid nitrogen can be used in the crop breeding programmes

Tapetum is important for the nutrition and development of pollen grains, as well as a source of precursors for the pollen coat.